In general, an image sensor is a semiconductor device for converting optical images into electric signals, and is mainly classified as a charge coupled device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS) image sensor.
A CMOS image sensor typically includes a photodiode and a MOS transistor in each unit pixel, and sequentially detects the electric signals of each unit pixel in a switching mode to generate images.
A CMOS image sensor includes a plurality of pixels to detect light. The pixels often include a photodiode, a plurality of transistors to drive the photodiode, an interlayer dielectric layer covering the photodiode, color filters provided on the interlayer dielectric layer corresponding to the photodiode, a planar layer provided on the color filters, and a microlens provided on the planar layer over the color filters.
The pixels of the CMOS image sensor are disposed in an active region, and a light blocking region is typically formed in the vicinity of the active region. In the light blocking region, the color filters often overlap with each other to block incident light.
Since the planar layer covers the color filters overlapping with each other, the planar layer is often very thick, thereby reducing the incident light in the photodiode.